Switching device



March 2, 1943. c. E. POLLARD, .JR 2,312,672

s'wITcHING DEVICE Filed May 9, 1941 9 mwnanllannrrunfll@ A Y /M/ENTOR C.E. POLL/4R0, JR

A TTORNEV Patented Mar. 2,1943

UNITED. f's'rprres Parri-:NTA oFFlca SWITCHIN G DEVICE Charles E.Pollard, Jr., Hohokus, N. J., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a. corporation of New York ApplicationMay 9, 1941, serial No. 392,655

7 claims. (ci. zoo- 97) This invention relates to switching devices andrelays and, more particularly, to those in which a conducting liquid,such as mercury, is used as the contact-making medium.

'I'he objects of the invention are to simplify devices of thischaracter, to render such devices more stable and resistant to shock andto render such devices responsive to small operatingl forces. It is wellrecognized that mercury has certain distinct advantages over solidelements as a contact-making medium for electrical circuits. Forinstance, a body of mercury presents a fresh surface for e'achsuccessive contact closure and is not subject to the pitting andcorroding effects that gradually reduce the usefulness of solid contactelements. With these advantages in view several forms of mercuryswitches have been devised in the past which may be divided into twogeneral classes. In one of these classes the container is tilted orotherwise moved to cause the body of mercury within it to shift itsposition thus opening or closing the desired connec-l tions. In .theother class an armature or other movable element is forced into a poolof mercury, the free surface of the mercury being displaced intoengagement with circuit-makingcontacts. In either case it has heretoforebeen necessary to move all or a considerable part of the mercury massinto a position in which it physically engages or disengages the desiredcircuit contact or contacts.

In accordance with the present -invention a very small mass of mercuryis employed which may be moved either by tilting the switch unit,subjecting it to the physical action or subjecting it to the influenceof a magnetic'field. In view of the small amount of mercury employedtheinertia of the mercury mass is small and the switch unit is thereforequickly responsive to a small operating force applied to the switchunit. The objects of the invention are attained by supporting two reedmembers parallel to and in close proximity to each other in an enclosingenvelope from a contact member extending into the envelope, betweenwhich reeds a small mass of mercury is held by adhesion to the adjacentsurfaces of the reeds which are of a material easily wettable by themercury. One -or more contact members may extend through the walls ofthe envelope into positions in which they may approximately midwaybetween the opposite ends of the reeds and out of contact with allcontact members except the contact member which supports the reeds. Ifthe switch unit is of the tiltable type the tilting of the unit willcause the mercury to move by gravity to a position at the depressed endsof the reeds into engagement with a contact member. If the switch unitis of the centrifugal type the rotation of the unit about an outsideaxis will causethe mercury to be forced by said centrifugal action tothe outer ends of the reeds where -it 'will engage a contact member. Theswitch unit may also be applicable to a relay structure in which thereeds may be-made of magnetic. material and attract-- able toward eachother when subjected to a. magnetic eld to force mercury from betweenthem into engagement with a contact member.

The invention is further applicable to replace the usual bubble elementof a spirit level. When so used the wettable reeds between which themercury is held are supported at each end by non-wettable supportssealed into the ends of a glass envelope. level the small bubble ofmercury is positioned midway between the ends of the reeds andcentralized with respect to the level indicating gauge line on the glassenvelope. o

For a clearer understanding of the invention, reference may be had tothe following detailed description taken in connection with theaccompanying drawing in which:

Figs. 1 and 2 disclose, in partial cross section, the normal andoperated positions, respectively, of a switch unit of the' tiltable orcentrifugal type constructed in accordance with the invention; Y

Fig. 3 shows a side view, partly in cross section, of a switch unit ofthe tiltable type which may be tilted in either one of two directions tocause the establishment of a connection through the mercury with eitherone of two contact members;

Fig. 4 shows a bottom view partly in cross section of the switch unit ofFig. 3;

Figs. 5 and 6 show, in partial cross section, the normal and operatedpositions, respectively, of a switch unit in accordance with theinvention andv operable by magnetic means; and

Fig. 7 shows a side View partly in cross section of an application ofthe invention to a spirit level.

Having reference rst to Figs. 1 and 2 of the drawing, the switch unitdisclosed therein com" prises a glass envelope I through one end ofwhich is sealed a contact member 2 and through the With the envelopeperfectly other end wall of which is sealed a second contact member 3.Welded or otherwise secured to other toward the end of the contactmember 3 are two thin reeds 4 and 5, the adjacent surfaces of which areof material, such as nickel, wettable by mercury. The free ends 6 and 1of these reeds are flared outwardly over the end of the contact member 3but out of engagement therewith. The space between the reeds is lledwith mercury 8 to the point where they spread apartvas disclosed in Fig.1.

When the switch unit is vibrated about a pivotal point, such asindicated by the point 9, centrifugal force will drive the mercurycolumn out into the position illustrated in Fig. 2, since the contactmember 2 being of material non-wettable by the mercury will not hold themercury against the centrifugal force acting upon it. In this positionthe mercury will engage the contact member 3 thereby establishing aconnection through the mercury, between the contact members 2 and 3.'When the oscillation ceases the surface tension of the mercury willsnap it backinto its original position illustrated in Fig. 1. The timeconstants of this switch unit are determined by the length and mass ofthe mercury column and by the stiiness of the mercury drop formedbetween the flared ends of the reeds.

By proper design this switch unit may be made to operate over a range offrequencies and time constants. One of the chief advantages of a switchunit of this character is that the mercury column is held withconsiderable force between the reeds and if, due to shock, some of themercury becomes displaced momentarily, it will, due to the surfacetension, return to its proper position between the reeds. To insure thisthe envelope fits the reeds as closely as possible.

The switch unit of Figs. 1 and 2 may also be, operated as a tilt typeswitch. When so operated the free flow of mercury between the wettedsurfaces of the reeds 4 and 5 added to the fact that by proper design abalance of surface tension forces may be obtained between the reeds andthe wetted end of the contact member 3, allows great sensitivity to beobtained by moving only a small amount of mercury.

Figs. 3 and 4 illustrate a modification of the switch unit for thepurpose of securing a double throw tilt type switch. In this modicationtwo contact members I2 and I3 are sealed in alignment through theopposite end walls of the envelope II and a third contact member I4 isalso sealed through one end wall of the envelope II and extends to apoint midway of the length of the envelope where it is bent at rightangles to 'afford a support I5 for two parallelly disposed reeds I6 andI1 which are welded or otherwise secured thereto at the mid-point oftheir length. The supporting end I5 of the member I4 lies in the planeofthe contact members I2 and I3 so that the reeds I6 and I1 aresupported with their flared ends embracing but out of engagement withthe ends of members I2 and I3. The inner surfaces of the reeds I6 and I1are of a material, such as nickel, which is wettable by mercury and acolumn I8 of mercury is held by f surface tension in a mid-positionbetween the ends of the reeds and in engagement with the contact memberI4 when the switch unit is held in its normal or horizontal position.

Should the right end of the switch unit be depressed, the mercury columnI8 will flow along the reeds to a position between the right ared themember.- 2 and extending parallel to each' ends thereof and intoengagement with the con- I Atact member I3. Should the left end of theswitch unit be depressed the mercury column I8 will flow along the reedsto a position between the left flared ends thereof and into engagementwith the contact member I2. When the switch unit is returned from eitherdepressed position to a horizontal position the mercury will by surfacetension move back into the original position at the central portion ofthe reeds.

The invention is also applicable in accordance with a furthermodification thereof disclosed in Figs. 5 and 6, for magnetic operationas the switching unit of a relay structure. This switch unit comprisesan envelope 2l through the opposite end walls of which two contactmembers 22 and 23 extend in alignment with each other. Welded orotherwise secured to the member 22 and extending parallel to each otherare two reeds 2'4 and 25. 'Ihe portion of reed 24 which is secured tothe contact member 22 and the outer portion of reed are made ofnon-magnetic material whereas the outer portion of reed 24 and theportion of reed 25 which is secured to the contact member 22 are made ofmagnetic material. The flared outer ends of'both reeds embrace the innerend of contact member 23 but are out of engagement therewith and theyinnersurfaces of both reeds and the end of contact member 23 arewettable by mercury. It will be noted that the inner end of the magneticportion of reed 24 overlaps the outer end of the magnetic portion ofreed 25. .A short column 26 of mercury is held by surface tensionbetween the reeds in the position illustrated in Fig. 5. An energizingcoil 21 surrounds the envelope 2'I at such a point that the overlapping`magnetic poiitions of the reeds are positioned within the co When thecoil 21 is energized flux enters the magnetic portion of reed 24, flowsacross the air-gap between the inner end of such magnetic portion andthe outer end 'of the magnetic portion of reed25, and leaves by suchportion where- Aby the reeds are attracted toward each other to forcemercury out between the ared ends of the reeds into engagement with thecontact member 23 thereby interconnecting the contact members 22 and 23through the mercury as illustrated in Fig. 6. When the coil thereafterbecomes deenergized, the reeds move away from each other and themercury, due to its surface tension, returns between the reeds to theposition illustrated in Fig. 5.

The invention is also applicable as disclosed in Fig. 7 as the testingelement of a level to replace the usual spirit element. For this purposetwo supports 32 and 33 are sealed to the opposite ends of a glassenvelope 3i and have secured between /their inner ends two parallellydisposed reeds 34 and 35, the inner surfaces of which are wettable bymercury. The supports 32 and 33 are of a material which is not wettableby mercury. Disposed between the reeds is a short column 36 of mercurywhich, when the envelope 3l is in a perfectly level position is disposedat the midpoint of the reeds as indicated bythe gauge illustrated. Ifdesirable,v the envelope might be made invarious shapes and sizes and ofvarious materials; the shape, location and number of lthe contactmembers may be varied and various modiiications of the magneticstructure disclosed in Figs. and 6 may be used.

What is claimed is:

1. In an electric switch, an envelope, contact members extending intosaid envelope, a pair of reeds supported in parallel spaced relationshipwithin said envelope, the adjacent faces of said reeds being of a.material wettable by mercury, a. body of mercury held by surface tensionbetween said reeds and means for overcoming said surface tension tocause said mercury to move freely between said reeds to interconnectsaid contact members.

2. In an electric switch, an envelope, contact members extending intosaid envelope, a pair of reeds supported in parallel spaced relationshipwithin said envelope on one of said members and having theircorresponding ends nared away from each other to embrace the inner endof another of said contact members but out of engagement therewith, saidreeds having their adjacent faces made of a material wettable bymercury, a body of mercury held by surface tension between said reedsland normally out of engagement with said other contact member, and meansfor overcoming said surface tension to cause said mercury to protrudebetween the flared ends of said reeds to interconnect said contactmembers.

3. In an electric switch, an envelope, a pair of contact membersextending toward each other through the opposite ends of said envelope,a pair of reeds supported at one end on the inner end of one of saidmembers and extending in parallel spaced relationship towards said othermember and having their free ends flared away from each other to embracethe inner end of said other member but out of engagement therewith,4said reeds having their adjacent faces of a material wettable bymercury, a body of mercury held by surface tension between said reedsand normally out of engagement with said other contact member, and meansfor overcoming said surface ten'- ison to cause said mercury to protrudebetween the flared ends of said reeds to interconnect said contactmembers.

4,. In an electric switch, an envelope, a pair oi contact membersextending toward each other through the opposite ends of said envelope,.a third contact member, a pair of reeds supported in parallel spacedrelationship on said third contact member and flared away from eachotherat each end to embrace but not engage said other contact membersrespectivelly, said reeds having their adjacent faces made of a materialwettable by mercury, a body of mercury held by surface tension betweensaid reeds and normally out or engagement with said other contactmembers, and means for overcoming said surface tension to cause saidmercury to protrude between the flared portions of said reeds at one orthe other end thereo! to interconnect said third contact memn ber withone or the other of said other contact members.

5. In an electric switch, an envelope, a pair oi contact membersextending toward each other through the opposite ends of said envelope,a pair of reeds supported at one end on the inner end of one of saidmembers and extending in parallel spaced relationship towards said othermember and having their free ends flared away from each other to embracethe inner end of said other member but out of engagement therewith, saidreeds having their adjacent faces made of a material wettable bymercury, a body of mercury held by surface tension between said reedsand normally out of engagement with said other contact member, andelectromagnetic means for moving the free ends of said reeds toward eachother to cause said mercury to protrude between the flared ends of saidreeds to interconnect said contact members.

6. In an electric switch, an envelope, a pair of Contact membersextending towards each other through the oppositeends of said envelope,a pair of reeds supported at one end on the inner end of one of saidmembers and extending in parallel spaced relationship towards said othermember andhaving their free ends flared away from each other to embracethe inner end of said other member but out of engagement therewith,

said reeds having portions of magnetic material and having theiradjacent faces wettable by mertromagnetic mearm for causing said reedsto be.

come attracted toward each other to cause said mercury to protrudebetween the flared ends of said reeds to interconnect saidcontactmembers. 7. In an electric switch, an envelope, a pair oi'contact members extending toward each other through the opposite ends ofsaid envelope, a pair of composite reeds supported at one end on theinner end of noe oi said members and extending in parallel spacedrelationship towards said other member and having their free ends aredaway from each other to embrace the inner end of said other member butout oi en gagement therewith, one oi said reeds having its supported endmade or non-magnetic material and its free end made of magnetic materialand the other of said reeds having its supported end made of magneticmaterial and its free end made of non-magnetic material and having theiradjacent faces wettabie by mercury. a body of mercury held by surfacetension between said reeds and normally out of engagement with saidother contact member, and a coil surrounding said envelope andenergizable to cause said reeds to become attracted toward each other tothereby cause said mercury to protrude between the flared ends of saidreeds to interconnect said contact members. l

CHARLES P0?

